First-principles Investigation of the Phase Stability for Ba(B1/3 ′2+B2/3 ′′5+)O3 Microwave Dielectrics with the Complex Perovskite Structure

Abstract

The phase stability of Ba(B_1/3 ^′2+B_2/3 ^′′5+)O₃ microwave dielectrics with the complex perovskite structure has been investigated using first-principles calculations. Our calculations indicate that many Ba(B_1/3 ^′2+B_2/3 ^′′5+)O₃ (B^′2+=Co, Mg, Mn, Ni, Zn; B^′′5+=Nb, Ta) compounds in equilibrium should be fully ordered in the 1:2 B-site structure with space group P3m1 (D_3d ³). Our calculations disagree with the experimental result for Ba(Mn_1/3Nb_2/3)O₃, but is consistent with many experimental obsernations for other Ba(B_1/3 ^′2+B_2/3 ^′′5+)O₃ compositions. The correlation between order-disorder phenomena and several characteristics has also been discussed. We find that the greater the stability of the ordered 1:2 structure with respect to the disordered phase, the higher the experimentally measured microwave Q-factor. It is found that neither both ionic radius difference and electronegativity differences between the B^′ and B^′′ ions have any relationship to phase stability. Also, our results show that B-site cation ordering causes cell distortion and more stable phase of ordered structure can enhance cell distortion.